The act of undermining someone else's opinion subtly, yet in a public area, to make him/her appear foolish.

The exhaust shaft is only two metres wide, so you'll have to use proton torpedoes.
Rebel Pilot: But that's impossible, even for a computer!
Luke Skywalker: It's not impossible - I used to bulls-eye womprats in my T-16 back home and they're not much bigger than two metres.
Sandbagged.

Knocked down or bowled over by a nasty or disparaging comment from someone you thought you could trust, with damage to your reputation or prospects.

Here’s the image: Two or more friends are tossing light objects to one another, and you get used to catching them easily. But then your “friend” tosses you a heavy sandbag, propelled with some force. You try to catch it, but it’s way more than you expected, and it knocks you flat on your back. You feel like a fool for being knocked over and for trusting that person in the first place.

Example: I thought I was OK with him - I even thought we were friends - but then he sandbagged me with a nasty comment, in front of people who are important to me.

What the girlfriend of your buddy does to you when she has no friends and you hang out with her, but she then goes home and tells your buddy that you did nothing but talk about his ex girlfriend. Which you didnt. But he takes her side because she gives it up to him. causes your buddy to freak out and start hurting people.

She totally sand bagged us after dinner. She went right home and complained to her boyfriend that we were talking about his ex or some shit. She's a total sand bagger!